1. Field of the Invention
The present invention relates to an imaging apparatus (an image pickup apparatus) for imaging and recording, for example, still images and moving images. More specifically, the invention relates to methods for controlling and starting up an electronic viewfinder system included in the imaging apparatus.
2. Description of the Related Art
Various types of imaging apparatuses, such as digital still cameras and camcoders, for recording and reproducing still images and moving images stored on a recording medium such as a memory card or a magnetic tape having a solid-state memory element are already commercially available.
An imaging apparatus including an electronic viewfinder including a liquid crystal panel is also commercially available. A virtual image on a two-dimensional display element can be viewed through the electronic viewfinder, which typically comprises a combination of the two-dimensional display element, such as a transmissive liquid crystal display or a reflective liquid crystal display, and an eyepiece optical system.
Recently, high-definition has been required for the images viewed through such an electronic viewfinder. To achieve this requirement, a predetermined number of pixels corresponding to the required image quality must be provided on the two-dimensional display element. Since the number of pixels provided in the two-dimensional display element increases, the number of failed pixels among the provided pixels increases as well. Furthermore, production of the two-dimensional display element becomes difficult because the size of the individual pixels become smaller relative to the size of the entire two-dimensional display element. Moreover, since the liquid crystal included in a two-dimensional display element has a slow response speed, an after image is generated when a moving image is displayed on the two-dimensional display element.
Instead of a two-dimensional display element, an image display apparatus for displaying an image by scanning beams of light emitted from a light source by a two-dimensional light-scanning mechanism is disclosed in U.S. Pat. No. 5,467,104. U.S. Pat. No. 5,467,104 discloses a technology for forming an image directly on the human retina by scanning red, blue, and green beams of light in two-dimensional directions (e.g., horizontal and vertical directions) and by using an optical system.
Such a technology does not require pixels to be formed in accordance with a predetermined resolution for scanning one light beam, as required for a two-dimensional image display element. Furthermore, pixel failure does not occur in principle.
In realizing such a scanning-type image display apparatus, a micro electro-mechanical system (MEMS) produced by a semiconductor process and used as light-scanning mechanism has been receiving attention. The light-scanning means produced based on such a MEMS technology is compact, light weight, and operable at high-speed. Such advantages are suitable for use as light-scanning mechanism for an image display apparatus. A light-scanning mechanism based on such MEMS technology is disclosed in Japanese Patent Laid-Open No. 07-175005 (corresponding to U.S. Pat. No. 5,606,447) and Japanese Patent Laid-Open No. 08-334723. Similarly, a MEMS device used as two-dimensional scanning mechanism for a head-mounted display was introduced at the Society of Photo-Optical Instrumentation Engineers (SPIE), Conference #4407-19 (June 2001, “Wafer Scale Packaging for a MEMS Video Scanner”).
The light-scanning mechanism based on MEMS technology performs scanning by polarizing light entering a reflecting surface tilted by torsion generated when a torsion bar is mechanically resonated. Since torsion is used, the light-reflecting surface does not rotate, but rather oscillates.
The fundamental frequency for such a mechanical resonance is determined by the mechanical size of the light-scanning mechanism. The light-scanning mechanism functions by being resonated by an electrostatic force or an electromagnetic force.
U.S. Pat. No. 5,467,104 discloses a two-dimensional scanning method in which a light-scanning mechanism is provided to perform light-scanning by resonance in a first direction and then another light-scanning mechanism is provided to perform scanning in a second direction.
However, a light-scanning mechanism based on such MEMS technology requires a predetermined amount of time until the driving control stabilizes because the light-reflecting surface is resonated by an electrostatic force or an electromagnetic force. Therefore, an imaging apparatus having an electronic viewfinder using such light-scanning mechanism requires a predetermined amount of start-up time.
Furthermore, an electronic viewfinder system using such a light-scanning mechanism consumes a large amount of electricity for the light source of the light beams used for scanning. Therefore, it has been a pressing issue to extend the operating time of a primary battery, such as an alkaline battery or a lithium battery, and a secondary battery, such as a NiCd battery, NiMH battery, or a Li battery, by reducing electricity consumption.